Integrated circuits include millions of active devices interconnected to form functional circuits and components. To form the interconnection structures, in one conventional semiconductor manufacturing process, metallized vias or contacts are formed by a blanket metal deposition followed by a chemical mechanical polish (CMP) step or, alternatively, an electrochemical mechanical polishing (eCMP) step.
Being more specific, in one known fabrication process, via holes are etched through an interlevel dielectric (ILD) to interconnection lines or a semiconductor substrate. Next, a thin adhesion layer such as tantalum nitride and/or tantalum is generally formed over the ILD and is directed into the etched via holes. Then, a metal film is blanket deposited over the adhesion layer and into the via holes. Deposition is continued until the via holes are filled with the blanket deposited metal. The deposition process, however, causes metal such as, for example, Cu, to be deposited on the surface of the wafer. The Cu thickness varies across pattern densities for example more Cu is deposited on high density areas
As is known, it is necessary to remove the excess metal on the surface of the wafer. Such removal can be accomplished using a chemical mechanical polishing (CMP) or electrochemical mechanical polishing (eCMP). In known eCMP process a small metal anode is placed on the center of the polishing pad. The edge of the wafer is continuously contacting the anode. The pad is perforated and with the conductive electrolutic solution contacts the cathode on the back of the pad and forms a closed circuit. This method requires that a continuous layer of Cu is across the wafer to maintain a closed circuit. Once islands of Cu are formed the circuit opens and removal stops. Therefore, is used to only remove the bulk Cu leaving approximately 2000 A to be removed on another platten by conventional CMP.
To remove the metal from the surface of the wafer, a current is applied to the cathodes and anodes of the conductive pad, while pressure is maintained against the surface of the wafer. During the polishing process, the pad and wafer are rotated with respect to each other. An abrasive and chemically reactive solution, commonly referred to as a “slurry”, as well as an electrolytic solution, is applied to the conductive pad during polishing. The slurry initiates the polishing process by abrading and chemically reacting with the film being polished; whereas, the electrolytic solution closes the circuit between the anodes and cathodes of the conductive pad. As current is passed between the cathodes and anodes, the metal on the wafer surface is dissolved by the anode.
However, in current processing,-the anode is conducting the edge of the wafer during a polishing process, the anode cannot make contact with metal islands on the surface of the wafer after the bulk copper is removed and islands start to form. That is, these metal islands, which are isolated, do not make contact with the anode and, as such, are not dissolved by the anode. This being the case, it is not possible, with known tools, to polish the entire surface of the wafer.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.